Change of residual strains in arteries due to hypertrophy caused by aortic constriction

The stress and strain that remain in an organ when the external load is removed are called residual stress and strain. They can be revealed by cutting up the organ in such a way as to reveal the zero-stress configuration. The function of the organ depends on the residual strain. For a blood vessel, the zero-stress configuration is very different from that of the no-load condition, and it changes over time when the physical stress acting on the vessel is changed. Data on rat aorta are presented. Physical changes were obtained by constricting the aorta at the celiac trunk level with a band of metal. Banding causes an increase of blood pressure and hypertrophy of the vessel in the upper body and a transient decrease of blood pressure in the lower body. If the aorta is cut transversely into rings and each ring is cut radially, it will open up into a noncircular arc, which may be characterized by its opening angle. It is shown that the opening angle varies systematically along the aorta and that it changes significantly together with changes of blood pressure and hypertrophy. In the ascending aorta, the opening angle increased from 171 degrees and to 214 degrees in 4 days after banding, then decreased gradually to an asymptotic value of 126 degrees in 40 days. At other sections, the swing of opening angle is smaller. The implications are discussed.